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Impact of Surface Hydroxylation on Stability of Silica-Support Metal Nanoparticles: On the Way to Tailor the Catalysts

Wanling, Zhu (2017) Impact of Surface Hydroxylation on Stability of Silica-Support Metal Nanoparticles: On the Way to Tailor the Catalysts. Master's Thesis, University of Pittsburgh. (Unpublished)

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Abstract

Catalysts lie in the central role in chemical reactions and act as the heart of countless chemical protocols, from academic research at laboratories scale to the chemical industry level. Nanocatalysts are the catalysts composed of nanoparticles, usually have some active metal nanoparticles sit on some types of the supports. Metal nanoparticles (NPs) are characterized by a very high surface area to volume ratio and a large number of low coordination sites. These properties make them highly desired act as active components in catalytic reactions and other applications. However, this high number of low coordination sites also strongly destabilizes particles and makes them prone to sintering then leads to the loss of active surface area, reaction activity and selectivity.

Recently, computational simulations from our group developed the amorphous silica model as the support in platinum-silica catalyst system using a combination of classical molecular modeling and density functional theory (DFT) calculations. In those studies, nanoparticle adhesion energetics and charge transfer were both found to be depend on the silica surface hydroxyl density. Since the hydroxylation is easily tunable by pretreatment temperature, this suggest that both electronic charge and catalyst stability can be modified via catalyst calcination.

In this work, the platinum NPs dispersed on amorphous silica support were used as model catalysts. Two silica supports with different hydroxyl densities were investigated to explore the impact of surface hydroxylation on stability and reactivity of the catalysts.

Through particle size analysis obtained by X-ray diffraction (XRD) and transmission electron microscopy (TEM) after elevated temperature treatment, we found that Pt NPs on fully hydroxylized silica is more stable than on dehydroxylized silica, with NPs on the former growing to only around half the size compared to those on dehydroxylized catalysts at 800 ºC.

Finally, we analyzed the reactivity of these two catalysts in CO oxidation and found that the ignition temperature of dehydroxylized catalysts was about 30 ºC higher than that of the rehydroxylized catalysts, which correlates well with improved thermal stability of this catalyst.

Overall, our results confirm that the degree of surface hydroxylation of silica has strong impact on both stability and reactivity of the silica-supported metal nanocatalysts.


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Details

Item Type: University of Pittsburgh ETD
Status: Unpublished
Creators/Authors:
CreatorsEmailPitt UsernameORCID
Wanling, Zhuwaz10@pitt.eduwaz10
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Thesis AdvisorVeser, Götzgveser@pitt.edugveser
Committee MemberJacobs, Tevistjacobs@pitt.edutjacobs
Committee MemberMcKone, James R.jmckone@pitt.edujmckone
Date: 25 September 2017
Date Type: Publication
Defense Date: 30 May 2017
Approval Date: 25 September 2017
Submission Date: 6 July 2017
Access Restriction: 5 year -- Restrict access to University of Pittsburgh for a period of 5 years.
Number of Pages: 87
Institution: University of Pittsburgh
Schools and Programs: Swanson School of Engineering > Chemical Engineering
Degree: MS - Master of Science
Thesis Type: Master's Thesis
Refereed: Yes
Uncontrolled Keywords: silica support, catalysts, metal catalysts
Date Deposited: 25 Sep 2017 20:13
Last Modified: 25 Sep 2017 20:13
URI: http://d-scholarship.pitt.edu/id/eprint/32696

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